For the degreasing of worked parts and precision parts having a large amount of mineral oils and fats attached thereto, metallic parts which are liable to stain or rust, small parts which are handled in a large amount in a cleaning basket, etc., chlorine solvents have been heretofore used for the most part, particularly 1,1,1-trichloroethane, which is a non-aqueous chlorine solvent excellent in properties such as high degreasing power and incombustibility.
In recent years, however, social awareness of global environmental issues has been increasing more and more, and this has led to a growing trend toward severer control on the discharge of environment-destroying substances. For example, 1,1,1-trichloroethane, which has been used in great quantities as an excellent degreasing detergent, is now on the list of substances destroying the ozone layer in the stratosphere. It was decided that the production of 1,1,1-trichloroethane shall be abolished by the end of 1995. Further, other chlorine solvents such as trichloroethylene and perchloroethylene involve environmental problems such as toxicity and contamination of underground water and have thus been gradually placed under restrictions. Accordingly, less pollutive substitute detergents for these chlorine solvents have been keenly demanded.
It is well known that a certain kind of bromohydrocarbon has a high dissolving power for various oils. For example, tribromomethane and 1,2-dibromopropane are described in JP-B-44-20082 (the term "JP-B" as used herein means an "examined Japanese patent publication"). 2,3-Dibromobutane and n-butyl bromide are described in U.S. Pat. No. 3,730,904. 1-Bromopropane and 2-bromopropane are described in JP-A-6-220494.
Among these bromohydrocarbons, 1-bromopropane is incombustible and has a detergent action equal to or higher than that of 1,1,1-trichloroethane but is disadvantageous in that it is liable to cause decomposition reaction induced by various metals such as aluminum, zinc, iron and copper.
The decomposition reaction of 1-bromopropane upon contact with a metal proceeds differently by the kind of the metal. This decomposition reaction shows a marked progress upon contact with aluminum. At ordinary temperatures, this decomposition reaction proceeds very slowly. Upon heating, this reaction involves a chain decomposition reaction while producing hydrogen bromide that eventually vigorously corrodes aluminum to convert 1-bromopropane to a dark brown tar substance. Accordingly, the essential requirement for the use of 1-bromopropane in the cleaning of various metallic parts is the stabilization of 1-bromopropane such that the decomposition of 1-bromopropane induced by various metals, particularly aluminum, is inhibited to prevent the materials to be cleaned and the cleaning apparatus from being corroded.
As an approach for inhibiting the decomposition reaction of 1-bromopropane induced by aluminum there is disclosed in JP-A-6-220494 a method which comprises the use of nitroalkanes, ethers, epoxides or amines singly or in combination as a stabilizer. However, the stabilizer composition disclosed as an example in the above cited Japanese patent application is disadvantageous in that it is not necessarily stable to metals commonly used as industrial metallic materials such as zinc, iron and copper and thus can corrode the materials to be cleaned or cleaning apparatus when used at high temperatures over an extended period of time, such as in vapor degreasing.